Microfibrous Composition Comprising Siliceous Spicules Of Spongiaria, Processes And Equipment For Obtaining Them

ABSTRACT

A microfibrous composition is described, particularly used for heat and sound insulation, which comprises an amount of siliceous spicules of spongiaria ranging from 70% to 99% by weight, based on the total weight of the composition. Further, the process and equipment designed to obtain said microfibrous composition are described.

This application claims priority of Brazilian patent application No.P10304176-0, the disclosure thereof being hereby incorporated byreference.

The present invention relates to a composition of microfibrous textureessentially comprising siliceous spicules of spongiaria, as well asprocesses and equipment for obtaining them. Said microfibrouscomposition may be used, among other uses, for thermal insulation. Thetechniques involved in the making of it are related to the ceramicindustrial sector and the sector of manufacturing artifacts for civilarchitecture.

Description of the Prior Art

Bodies composed by fibers, for example from animal hair, are mostly goodthermal insulators. So, various products constituted by natural fibersare utilized. In the animal kingdom there are sheep wool, furs fromrabbit and other animals. In the vegetable kingdom, there are woodenfibers, from which paper and cardboard are made, and other, such ascotton fibers to make various fabrics. In the mineral kingdom, there areproducts such as chrysotile, ordinarily called amianthus.

Various fibrous synthetic products have arisen and are good products forheat and sound insulation. Among them, polymeric fibers such as nylonand polyesters stand out. In a field of use for insulation designed forhigher temperatures, glass fibers, “rock wools”, calcium silicate fibersand also the so-called “ceramic fibers” have appeared.

In addition to the fibrous form, there are also insulants having highporosity, such as corks of vegetable origin, expanded polystyrene andpolyurethane, besides kaolin-based and/or diatomite-based insulants.

Focusing now on the filed of high-temperature fibrous insulators, it canbe noticed that amianthus is a very interesting product, but there istoday serious restrictions to the use thereof, mainly due to questionsof salubriousness. Since this product is expected to go out of themarket, only the above-mentioned synthetic fibers will be left.

The glass fibers are relatively noble products and may be long,continuous or short filaments, of great chemical and physicalhomogeneity. They resist up to 800° C. and are commercialized in webs,being relatively expensive.

The calcium silicate fibers are less expensive fibers, but are intendedto be used at temperature no higher than 600° C. They are also sold inwebs or as semi-rigid aggregate products.

The “rock wools” are products derived from the basaltic rock melting.They sand temperatures around 800° C. and are cheaper than glass fibers.They are commercialized in webs or in semi-rigid pieces. Such productstoday are often used in domestic and industrial ovens such as bakeriesand also in insulation of solar heater.

The “ceramic fibers” are more refractive having types which standtemperatures from 1.250° C. to 1.400° C., being some of them able tostand even higher temperatures. They have, generally, silico-aluminousto aluminous composition, and their refractoriness increases accordingto the amount of aluminum comprised therein. There is also the puresilica fiber with good refractory properties. The costs of themanufacturing theses fibers depend on their deterioration resistanceunder high temperatures. Generally, all types of this fiber have goodthermal insulation properties. However, theses fibers, under hightemperatures, deteriorate by melting or get fragile by recristalizationmainly of christobalite in the glass mass. The ceramic fibers arecommercialized in long fibers constituting webs, or then, in shortfibers, generally, aggregated by resin binding components constitutingsemi-rigid products.

Ceramic fibers exhibit, as a restriction to its use, low compressionstrength or bending strength, even in the so-called “rigid” products,and a high linear retraction of up to 8%, found in the first burning attemperatures of continuous use. In addition, such products are quiteexpensive with respect to other high-temperature insulators.

The microfibrous composition of the present invention comprisessiliceous spicules of spongiaria (explained in greater detail later) andoften look like synthetic products constituted by short ceramic fibers.

Siliceous spicules of spongiaria are cylindrical microneedles withlength on the order of 500 μm, thickness on the order of 10 μm,essentially composed of silica. Such spicules can be qualified as fibersor microfibers due to said dimensions. Such terminology will be usedhereinafter, in this context.

Said siliceous spicules of spongiaria are parts remaining from skeletonsof colonies of certain organisms that are scientifically called sponges.Sponges are minute animals of aquatic life, which form colonies calledspongiaria. Cyclically, the colonies die, releasing the spicules thatare dispersed in the aquatic medium, settling on the beds of lakes orsea, and are then fossilized. This process, which occurs after tens orhundreds of years in the same biological medium, enables the formationof expressive deposits of these materials.

Important concentrations of spicules of sponges are found in sedimentaryextracts of specific geological environments, always mixed with clays,sands and other materials predominantly of aquatic organic origin. Rocksrich in these materials receive the geological name “spongilites”, beingordinarily known, in Brazil, as “barro de pó de mico” or simply “mico”which corresponds to their appearance similar to fine hairs.

Ceramic products derived from materials constituted by siliceousspicules of spongiaria are widely known. By way of clarification, thefollowing is reported:

-   -   a) since before Brazil was discovered, certain indigenous tribes        had already used materials derived from sponges in ceramic        craftwork for making highly resistant pots intended for cooking        food;    -   b) in Brazil a pottery industry exists since centuries ago,        which is based specifically on these materials. At present, it        is estimated that in this country about 50,000 families make a        living in this activity, scattered in small communities, some of        them with over 5,000 inhabitants, always located near of around        natural deposits;    -   c) the ceramic pieces, made from these materials, being        preferably bricks, are characterized by their high strength,        their heat-insulation properties and some refractoriness; by        virtue of these properties, they are used in civil architecture,        in making ceramic furnaces, barbecues and charcoal-industry        furnaces, among other possibilities. They are ordinarily known        as “tijolos de mico” or “tijolos de pó de mico”;    -   d) the formulations used, for example, for making ceramic pieces        are most varied, depending upon the availability of ores at the        place or at the moment. So, according to the place or time, the        production of pieces varies much from pieces very rich in        microfibers with up to about 50% (by weight) to pieces very poor        in microfibers with from 5% to 10%. Clays and sands, which occur        close to the microfibers in ores, constitute the rest of the        formulations, with few exceptions. These natural concentrations        of microfibers of spongiaria are not sufficient for providing        pieces with excellent heat and sound insulation properties.

Microfibers are considered the strong point of these materials. So,products having the useful properties, optimized from microfibers weredeveloped, thus obtaining levels of industrial conformity that meet thepresent-day specific requirements. In order to achieve the results knowntoday, the following steps were necessary:

-   -   a—development of technology for beneficiation of ores leading to        the separation of microfibers;    -   b—multiple assays on formulations and development and        optimization thereof;    -   c—systematic studies involving the shaping of pieces and        technical characterization of the microfibrous compositions        obtained on laboratory scale; and    -   d—development of technology for shaping and manufacturing        artifacts on an industrial-production scale.

With the study of these materials over these years, it has been possibleto obtain much purer concentrates thereof, that is to say, exhibitinghigh concentrations of spicules. With these concentrates, high-qualityinsulating pieces with the help of industrial shaping techniques can bemade, which are also the object of the present invention.

OBJECTIVES OF THE INVENTION

An objective of the present invention is to provide a microfibrouscomposition comprising siliceous spicules of spongiaria, the amountthereof ranging from 70% to 99% by weight, based on the total weight ofthe composition. This amount is much higher than that already obtainedin the prior art, and resulting in relevant improvements of thephysico-chemical properties inherent in the pieces made with thiscomposition.

Another objective of the present invention is to provide the processesand the respective equipment for obtaining the microfibrous compositionaimed at.

BRIEF DESCRIPTION OF THE INVENTION

The objectives of the present invention are achieved by means of amicrofibrous composition, particularly used for heat insulation andsound insulation, characterized by comprising an amount of siliceousspicules of spongiaria ranging from 70% to 99% by weight, based on thetotal weight of the composition.

The objectives of the present invention are also achieved by means of aprocess for obtaining the microfibrous composition, which comprises thefollowing steps:

-   -   a—mixing the microfibers with water and at least one binding        component in a friction tank;    -   b—stirring said mixture until a homogeneous pulp is achieved;    -   c—shaping the pulp in a shaping equipment to eliminate the        excess of water and binding components and to obtain a residual        cake;    -   d—curing the residual cake by a curing process, so as to obtain        the microfibrous composition.

Further, the objectives of the invention are achieved by means of anequipment to promote the shaping of the residual cake, which comprises:

-   -   a mold associated, at its upper part, to a container and, at its        lower part, to a bulkhead;    -   said mold being further associated, at its lower part, to a        liquid collector and to an outlet for the residual pulp.

The microfibrous composition presented now has many advantages over theproducts based on synthetic fibers and over the products that comprise alower concentration of siliceous microfibers, above all in heatinsulation, strength and dimensional stability when used at hightemperatures, some of which are listed below.

While some of the fibers of the prior art, such as glass fibers, “rockwools”, calcium silicate fibers, among others, are resistant totemperatures of up to 800° C., the microfibrous compositions of thisinvention exhibit heat strength at higher temperatures, reachingtemperatures of about 1,250° C.

It is possible to make larger and less dense pieces with themicrofibrous composition of the present invention, in comparison withthe pieces made from insulators of the kaolin/diatomite lines.

In comparison with ceramic-fiber compositions:

-   -   the microfibrous composition of the present invention exhibits        dimensional stability, configured by linear retraction in the        re-burning on the order of 1 mm/m, or 0.10%, whereas pieces made        from ceramic fibers exhibit values even higher than 4.5%.    -   The more rigid pieces of ceramic fibers mostly deform under        stress, unlike the pieces comprising the microfibrous        composition of the present invention, which exhibit rigidity        even to rupture.    -   With regard to the strength, measuring pieces having a specific        mass of 0.40 g/cm³, bodies composed of the microfibrous        composition of the present invention exhibit values on the order        of 0.47 and 0.41 MPa of compression strength and fending        strength, respectively, while bodies composed of ceramic fibers        exhibit compression strength on the order of 0.25 MPa and a        virtually null value with regard to the bending strength.    -   The pieces comprising the microfibrous composition of the        present invention exhibit heat-insulation properties very        similar to those inherent in the best ceramic-fiber pieces. For        example, at a temperature of the hot face on the order of 1,000°        C., pieces made from the microfibrous composition exhibit a heat        conductivity coefficient of 0.192 W/m.K, whereas an optimum        product constituted by ceramic fibers exhibit a heat        conductivity coefficient of 0.190 W/m.K.

Comparing the microfibrous composition of the present invention withcompositions made from rock wool and calcium silicate wool:

-   -   the microfibrous composition exhibits higher values of        refractoriness properties with respect to the pieces made from        rock wool and calcium silicate wool.    -   Further, it exhibits greater dimensional stability upon being        subjected to high temperatures.

With regard to the insulating products composed by kaolin/diatomite:

-   -   the pieces (bricks) made from kaolin/diatomite usually exhibit        dimensions corresponding to 224×112×76 mm. On the other hand, by        using the methods of making pieces explained in greater detail        later, it is possible to make larger pieces comprising the        microfibrous composition of the present invention, with at least        one of the dimensions even larger than 1.0 meter each.    -   It is possible to make pieces comprising the microfibrous        composition of the present invention exhibiting apparent        specific weight much lower in comparison with all the known        pieces made with kaolin and diatomite.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail withreference to embodiments represented in the drawings. The figures show:

FIG. 1 illustrates a flow diagram of the industrial processing forobtaining the microfibrous composition of the present invention;

FIG. 2 illustrates a first schematized embodiment of the equipment usedin the process of obtaining the microfibrous composition of the presentinvention;

FIG. 3 illustrates a second schematized embodiment of the equipment usedin the process of obtaining the microfibrous composition of the presentinvention; and

FIG. 4 illustrates a third schematized embodiment of the equipment usedin the process of obtaining the microfibrous composition of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The microfibrous composition of the present invention is composed ofmicrofibers of siliceous spicules of spongiaria and binding componentssuch as various kinds of clay. It is intended for uses the requirerefractoriness properties at high temperatures of up to 1,250° C. orhigher.

1—Microfibers of Spongiaria

The microfibers must be cleaned, loosened and sorted according to theirsize in order to be used in the microfibrous composition of the presentinvention.

In order to obtain microfibers free from natural impuritiesindustrially, ores are processed. The processes comprise hydration andattrition by using chemical dispersants, thus obtaining a pulp in whichgrains are sorted later. Sand and fine residues are removed byhydrocycloning and settling, respectively.

The microfibers may have varied shapes, that is, they may be constitutedby entire or fragmented original spicules, either mixed or not, as longas they exhibit the properties and characteristics listed below.Specific weight 2.0 to 2.2 g/cm³ Maximum length About 500 μm Averagelength About 200 μm Average thickness About 10 μm Length/thickness ratio10 to 20 Appearance Rectilinear, transparent, rigid micro- needlesMineralogical composition Amorphous silica, and it may exhibitchristobalite traces Morphologic composition Acicular (needles) withhollow core, cylindrical, very smooth, with both endings tapered whenentire Chemical composition Essentially SiO₂ (more than 98% aftercalcination) and impurities with Al₂O₃ from clay contaminants Loss infire 6 to 9% of volatile components (water and carbon dioxide)Pyrometric cone 1740 to 1760° C.

According to the properties and characteristics described above, thespicules of spongiaria are needles or acicules, the maximum length ofwhich is of 0.5 millimeters, being transparent, rigid, composed ofamorphous silica and volatile components. A ratio between length andthickness on the order of from 10 to 20 times and length smaller than0.5 mm enable them to be technically called fibers or microfibers.

2—Microfibrous Composition

As shown before, the microfibrous composition has a microfibrous textureand is essentially constituted by siliceous spicules of spongiaria. Ithas mainly the characteristics described below: Range of apparentspecific mass From 0.06 to 1.20 g/cm³ Average apparent specific mass0.50 g/cm³ Range of porosity 45 to 95% Average porosity 70% Maximumpyrometric cone 1740° C. Mineralogical composition Microfibers: morethan 70%, binding components: less than 30% Chemical composition SiO₂(after calcinations): more than 80% Al₂O₃ + Na₂O + FeO + others: lessthan 20% Loss in fire 0 to 10%Note:The mechanical properties of the microfibrous composition depend uponthe binding component chosen to be used in its composition.

The function of the binding component is to provide adhesion of themicrofibers. The main binding components that may be used in the presentcomposition are: aluminous clays, kaolinitic clays, smectitic clays,mixed clays, colloidal silica and silicic acids. However, other bindingcomponents may be used since they exhibit the characteristics necessaryfor the formulation of the microfibrous composition already described.

Tests carried out have shown a relative success with: aluminous clays,kaolinitic clays, smectitic clays, mixed clays or mixture thereof andcolloidal silica, among others. The choice thereof will be conditionedto the final destination of the microfibrous composition. In the fieldof heat insulators for high temperatures, for example, kaolinitic claysor aluminous clays may be used and, for low temperatures, smecticticclays.

The process of curing said microfibrous composition also varies,depending upon the binding component chosen. This process may be carriedout: in open air, in ovens or in calcining furnages.

The apparent specific mass of the microfibrous composition is a functionof the special arrangement of the microfibers, as well as of thedistribution of average sizes thereof. Values on the order from 0.40 to0.60 g/cm³ are more commonly obtained. For lower values, it is necessaryto apply procedures that open the microfiber mesh, as for example, byintroducing fillers with volatile components and, for higher values,procedures like the application of vibrations that cause approximationthereof, making the aggregate dense. Values from 0.06 to 1.2 g/cm³ havealready been obtained in this way.

The porosity is inversely proportional to the apparent specific mass, inthis case, with very high values, ranging from 45% to 95%.

The melting temperature of the microfibrous composition will depend uponthe type of binding component used. The microfibers, being ofessentially siliceous nature, have a melting point close to the meltingpoint of quartz, on the order of from 1740 to 1760° C. Bound bycolloidal silica, for instance, the microfibrous composition exhibitsmelting strength close to this value. Bound by kaolinitic clays, forinstance, the melting point will be on the order of from 1550 to 1600°C. Aluminous clays permit higher melting temperatures, on the order offrom 1600 to 1650° C. Bound by smectitic clays, there will be areduction in the melting point to about 1350° C.

The mechanical properties of the microfibrous composition will alsodepend upon the type of binding component used. There are destinationsfor which there is no interest in high mechanical performance, as is thecase of certain heat insulators for “back-up” furnaces, that is to say,those heat insulators that do not receive heat directly from the hottestportion of the furnace. On the other hand, there are cases in whichstrength is fundamental. Significant results may be achieved, forinstance, in pieces whose binding components are kaolinitic clayssterilized at high temperatures, reaching a pressure of up to 1.0 MPa ofbending for pieces with apparent specific mass of 0.50 g/cm³, which is asurprisingly value with respect to heat insulators available on themarket. In the following table, some results are shown, which wereachieved after calcinations at 1250° C., using various types of bindingcomponents. Bending Type of binding Apparent specific Cold compressionstrength component mass g/cm³ strength (MPa) (MPa) Kaolinitic clay 0.691.80 1.04 Aluminous clay 0.70 2.27 1.17 Smectitic clay 0.75 4.95 2.56Colloidal silica 0.82 0.95 0.26

It can be noticed that the best binding component to be used in theconstitution of the microfibrous composition is smectitic clay, when thewish is to obtain high values of strength.

In addition to the strength variation configured by the various types ofbinding components, there are naturally other variations that resultfrom the final apparent specific masses of the microfibrous compositionobtained. The table below illustrates the values of compression strengthobtained after burning, at a temperature of 1,250° C., test bodieshaving kaolinitic clays as binding components: Apparent specific mass(g/cm³) Cold compression strength (MPa) 0.20 0.15 0.30 0.40 0.40 1.000.50 1.80 0.60 2.60

It can be concluded then that, when the microfibrous compositioncomprises kaolinitic clay as a binding component, the cold compressionstrength increases proportionally with the increase in the apparentspecific mass.

The microfibrous composition generally comprises at least 70% ofmicrofibers and the rest of binding components. In most products, theamount of microfibers is higher than 90%, reaching 99% of thecomposition, and the remaining amount is of binding components, whichcompose an extremely thin film enclosing the microfibers.

Regarding the chemical composition, the amount of silicon dioxide rangesfrom about 80% to about 99.0%, and this latter value may be obtainedwhen siliceous chemical binding components are used, like colloidalsilica.

2.1 Examples of Microfibrous Composition

The microfibrous composition is basically composed of microfibers andbinding components, the microfibers being the main components, theamount of which ranges from 70 to 99%. Examples of microfibrouscomposition are described below (values in weight, dry base): Amount ofmicrofibers Type of binding component Example (% by weight) (% byweight) 1 70 to 95% 5 to 30% of kaolinitic clay 2 70 to 95% 5 to 30% ofaluminous clay 3 75 to 97% 3 to 25% of smectitic clay 4 70 to 95% 5 to30% of mixed clays 5 82 to 99% 1 to 18% of colloidal silica

The most usual composition for the production of articles havingexcellent heat and sound insulation properties preferably contain about90% by weight of microfibers. In case the binding component is colloidalsilica, this amount then becomes 96%.

Some more interesting examples for industry may be pointed out, namely:Amount of Amount of binding Type of binding microfibers componentExample component (% by weight) 9% by weight) 1 Kaolinitic clay 90 10 2Colloidal silica 96 4

The above examples are preferred embodiments of the microfibrouscomposition of the present invention and should not be taken aslimitations thereof. So, many variations of composition may be carriedout within the protection scope delimited by the accompanying claims.

3—Processes for Obtaining the Microfibrous Composition

The process for obtaining the microfibrous composition is illustrated inFIG. 1 and comprises the following steps:

-   -   a) a mixture of water and at least one binding components is        prepared in the proportions of from 80% to 90% of water and the        rest of binding components, obtaining the pulp called barbotine;    -   b) an amount of previously cleaned and loosened microfibers 1 is        added, together with the barbotine pulp at a ratio ranging from        1:3 to 1:5 in an attrition tank 2, provided with rotary tabs        driven by reducing mechanisms, to be mixed and homogenized so as        to yield a homogeneous pulp 4;    -   c) the pulp 4 is routed through tubes to a shaping equipment 5,        where the shape and the consistency of the microfiber        agglomerate are checked; settling processes with or without        vibrations, pressure or vacuum filtrations may be employed for        this purpose, according to the type of equipment 5, as will be        detailed later;    -   d) in the shaping equipment 5, a wet residual cake 6 is formed        with the arrangement of the fibers exhibiting a density on the        order of 0.8 to 1.0 g/cm³, varying according to the degree of        aeration to which the residual cake 6 is subjected, which        enables the handling thereof on special trays; the mixture that        comprises water and residual binding components 3 is eliminated        or recovered for recirculation;    -   e) the residual cake 6 obtained will undergo a curing process 7,        which is preferably carried out by drying in ovens; the drying        of the residual cake 6 obtained will render the products rigid,        imparting strength to them, resulting in the microfibrous        composition.

Optionally, the microfibrous composition obtained with the curingprocess 7 may then undergo a firing process 8 at temperatures of up to800° C., carried out in ceramic furnaces. This process is suitable forthe microfibrous composition the binding components of which are claysthat should be sintered at high temperatures. This firing process 8 maybe of the continuous type, with the use of tunnel furnaces or rollerfurnaces or else intermittent, using various types of furnaces, such asthe traditional type, called “demijohn furnace”, or others.

Further, the cured microfibrous composition, depending upon therequirements of the field of utilization, may be mechanically rectified,whereby warps and imperfections beyond the standard dimension areeliminated. Such grinding 9 is carried out by using grinders.

4—Equipment for Obtaining the Microfibrous Composition

The processes, presented in summary, are three:

-   -   a) settling including the variants “simple” or “with        vibrations”;    -   b) filtration under pressure, and    -   c) Vacuum filtration.

The settling process consists of the physical actuation of this processon pulps held in containers, called molds, during an interval of time ofabout 20 minutes per operation, resulting in a relatively rigid body,configured by the entanglement of the microfibers. Vibrations may beapplied in the course of the settling, promoting a decrease in emptyspaces between the microfibers, generating a microfibrous composition ofgreater relative density. Such obtained piece, depending upon thebinding component used and the proposed use, should be made rigid orcured by drying in the open air or ion ovens; such drying may or may notbe followed by a firing at high temperatures. This process will bedescribed in greater detail later.

On the other hand, the pressure-filtration process consists in obtaininga filtered cake, by forced passage of the pulps containing bindingcomponents and microfibers through a semipermeable partition, usually athin web, which contains the microfibers and part of the bindingcomponents. Such a filtered cake is wet, consistent to the extent thatit can be handled with shapes that are given by molds coupled to thesemipermeable partition. The pressure is provided by the compressed airto be injected in bell jars overlapping the web, or else by forcedpumping of the pulp itself. This process will be described in greaterdetail later.

Finally, the vacuum-filtration process is similar to that describedbefore, with the difference that the filtration accelerating agent isvacuum, which is applies in a hermetic chamber positioned below thesemipermeable partition. The cake obtained will also be subjected todrying and may also be fired at high temperatures, depending upon thechoice of the binding component and upon the destination thereof.

All the residual pulps of the three processes defined before are re-usedafter being reconditioned, the consumed portions of binding componentbeing replaced.

4.1 First Embodiment of Process and Equipment—Settling Process

The microfibrous composition may be obtained by means of a processcalled settling process, which consists in the actuation of this processon pulps containing microfibers, where water and the binding componentsare also mixed.

The shaping may be made by means of a simple settling process, whereinthe particles settle according to the viscosity of the pulp at speedsranging from 0.5 to 2.0 cm/min, resting on the bottom of the mold, ontop of each other, forming a settled cake. On the other hand, in thecase of settling under vibrations, unlike the simple settling, oneapplies vibrations of frequencies ranging from 0.02 Hz to 40 KHz,provided by mechanical, electric and also ultrasonic vibrators. Suchvibrations, applied to the molds, will be transferred to the settledcake, compacting it and generating the product different from thatobtained by simple settling.

At the end of the process, the overlaying pulp, now free from themicrofibers, may be eliminated. In the case of molds containing finewebs at the lower part, the elimination of the pulp may take place bypouring through the cake obtained, by gravity or by forced pouring, bymeans of vacuum chambers and pressure chambers coupled to the mold. Incase impermeable molds are opted, the residual pulp is removed bypumping or by outflow. The microfibers, which are settled on the bottom,intricate arrangements in a single, permeable cake, exhibiting densityon the order from 0.8 to 1.0 g/cm³, varying according to the degree ofaeration to which the residual cake is subjected, which enables thehandling thereof on special trays.

In FIG. 2, a schematic drawing of equipment designed for molding piecesby settling is illustrated, with or without application of vibrations,with removal of the residual pulp by pouring through the settled cake.

This equipment comprises a mold 10, where the mixture of themicrofibrous composition is held, at its upper part, a container 11 isapplied, intended to hold a large amount of pulp 4. At the lower part ofthe mold there is a partition 12, constituted by a very thin web, whichprovides a very slow outflow of permeable liquids in the settledmaterial. Below the partition 12, there is a liquid collecting trough13, which is welded to the mold 10; this trough 13 has a bore forletting out the residual pump 14 and, at its bottom, it may have acoupled vibrator 15. The whole equipment is supported by a spring device16, which may be composed of helical springs or rubber pads of highstrength, fixed to the bottom of the trough 13.

The mold 10 may be of any shape, as long as it will hold the volume ofpulp that comprises the microfibers and the binging component(s).Particularly, the mold 10 is triangular in shape with dimensions on theorder of 1.40 m×0.70 m. The container 11 may be of any shape that may beuseful to the equipment, that is to say, it may represent a spacecorresponding to the pulp volume to be processed. The web 12 ispreferably very thin, in order to provide better retention of liquid,including a product with less water, but the mesh aperture of the webmay vary according to the final product to be obtained. Preferably, oneuses a web made of stainless still in meshes of 60-200 mesh-tyler. Theliquid collecting trough 13 has the function of collecting the liquidremoved from the initial cake; so, its shape or size are not relevant.

In a molding operation, the pulp 4 containing known amounts ofmicrofibers and binding components (obtained by the process schematizedin FIG. 1) is placed in the mold 10. The pulp 4 remains setting for aninterval of time ranging from 20 to 30 minutes, so as to achieve thetotal settling of the particles and the outpour of the residual liquidsthrough the web 12, being collected by the trough 13 and eliminated bythe outlet 14. At this moment, vibrations may be applied by actuatingthe vibrator 15, which will make the whole assembly vibrate, from thespring device 16, which is preferably composed of helical springs,whereby the settled cake is made dense.

For removal of the intermediate product formed here, use manualtechniques or suitable mechanisms may be used. A manual techniqueindicated for removal of the intermediate product above consists inplacing a preferably metallic or wooden tray on it, securing it to theside of the mold, turning the whole equipment and supporting the tray onan easel. Once this has been done, the tray is released and theequipment is raised, while the filtered piece remains, now released fromthe mold, on the easel. This technique may be carried out mechanically;for this purpose, all you need is a turning mechanism at the wholeequipment via cranes and a mechanism for removing the tray by means of aplatform intended to collecting the tray containing the piece thereon,which moves vertically by mechanical actuation. The choice of the besttechnique for removing the intermediate product depends upon the typeand dimensions of the pieces to be made.

4.2 Second Variation of Process and Equipment—Process of FiltrationUnder Pressure

The process of filtration under pressure consists in applying pressureonto the pulps containing microfibers, forcing the passage thereofthrough a partition having small bores, generating a filtered, wet andconsistent cake that may be handled (it exhibits a density on the orderof 0.8 to 1.0 g/cm³, varying according to the degree of aeration towhich the residual cake is subjected), the shape of which is given bymolds coupled to the partition.

The filtration under pressure is an intermittent process, in whichpressure on the order of 0.5 kg/cm² is applied, which will promoteacceleration of the process. This operation consists in the forcedpassage of the pulp through partitions having small bores, smaller than0.30 mm. Such partitions may be webs made of steel, organic materialssuch as fabrics, sleeves or plastic webs, or else papers suitable forfiltration. Two mechanisms are used for applying pressure: introductionof compressed air and hydrostatic pressurization by pumping the pulp;this latter case is similar to filtration in sleeve filters. Thepressure applied will depend upon the mechanism used, and it iscommonplace to use pressure values on the order of 0.2 to 10.0 kg/cm2.

At the end of the filtration under pressure, the microfibers become awet cake with some consistency (density on the order of from 0.8 to 1.0g/cm³), which enables the handling thereof on special trays. On theother hand, the mixture that comprises water and binding components,resulting from the filtration, is eliminated or recovered forrecirculation.

In FIG. 3, one illustrates a schematic drawing of a filter driven bypressurized air. A filter is usually composed by two main pieces: upperbells 17 and mold 18. The upper bell 17 is a container large enough forholding the amount of pulp 4 of a filtration operation; one insertedinto it a feed tube 19, which has a coupled diaphragm 19 a, whichautomatically closes when the upper bell 17 is pressurized. Also at thisupper bell 17 there is an inlet 20 for compressed air and a safetymanometer.

The mold 18 is a reinforced piece having, at its bottom, a thin web 22and a lower container for collecting residual pulps 23, in which a tube24 is installed for discharging such pulps. Between the upper bell 17and the mold 18 there are moveable claws 25 intended for joining ordisjointing the joining of both pieces.

In filtration operations, the pulp 4, the volume of which is previouslymeasured, is introduced in the machine through a feed tube 19 until thedesired amount is reached. Compressed air under controlled pressure isinjected, which will actuate the diaphragm 19 a, closing it andpressurizing the upper bell 17. The pressure then forces the passage ofthe liquids through the single outlet, which is the web 22 situatedbelow the mold 18, forming a filtered cake on said web 22, and theresidual pulp flows through the lower container 23, being discharged bythe outlet tube 24.

The filtration process ends when only compressed air comes out of theoutlet tube 24. At this moment, the compressed-air inlet should beclosed, disjointing the movable claws 25, the upper bell 17 and thefiltered piece should be removed.

The mold 18 may have any shape, as long as it can hold the pulp volume,which comprises the microfibers and the binding component(s). Thecontainers 17 and 23 may have any shape that is useful for theequipment, that is, they may have a space corresponding to the pulpvolume that is to be worked on. The web 22 is preferably very thin inorder to promote better retention of the liquid, yielding a product withless water, but the aperture of the web mesh may vary according to thefinal product that is to be obtained. By preference, a web made ofstainless steel in meshes ranging from 60 to 200 mesh-tyler is used.

The mold 18, as well as the bell 17, have particularly rectangularshape, with dimensions on the order of 1.40×0.70 m, being hermetic toleakages of liquids or compressed air. They consist of robust pieces, ofsteel, at least 5 mm thick, made to bear high pressures. The movableclaws 25 are very resistant pieces, being constructed to bear pressureshigher than 15 tons.

4.3 Third Variation of Equipment—Vacuum Filtration Process

The vacuum filtration process is an intermediate process, wherein thevacuum causes acceleration of the filtration process. This operationconsists of the forced passage of the pulp through partitions havingsmall bores of less than 0.30 mm. Such partitions may be of steel,organic materials like fabrics, sleeves or plastic webs, or else paperssuitable for filtration.

In a closed chamber, located below the partition, vacuum is applied, soas to bring about suction of the pulp through the partition. Themicrofibers are retained on the partition, and the other liquids are letthrough the newly formed cake, settling in the lower chamber. Theprocesses end when the whole overlying liquid has been sucked and onlyair passes through the filtered cake.

With these mechanisms, the vacuum is generated by a conventional vacuumpump. For dynamism and rapidity of the process, the industrial plantshould have a reservoir where large volumes are accumulated withdifference in negative pressure.

At the end of the filtration, the microfibers become a wet cake withsome consistency (density on the order of 0.8 to 1.0 g/cm3), whichenables the handling thereof on special trays. On the other hand, themixture containing water and the binding component(s) resulting from thefiltration is eliminated or recovered for recirculation.

In FIG. 4, a schematic drawing of a vacuum-actuated filter isillustrated. It is basically composed of three main pieces: a pulpreservoir 26, a mold 27 and the vacuum chamber 29.

The reservoir 26 is a container totally open at its upper part,sufficiently large to hold the amount of pulp of a filtration operation,which is coupled to the mold 27 at its lower part. The mold 27 is closedat its lower part by means of a partition 28, which may be, for example,a very thin screen. Below the partition 28 there is a closed chamber,called vacuum chamber 29, which has a coupled diaphragm 30 thatautomatically closes when vacuum is applied to the chamber. In order tobring about vacuum in the chamber 29, it is necessary to introduce avacuum conduit 31, which can make the communication between the chamber29 and the vacuum reservoir 32. In the chamber 29, a vacuum gauge 33 maybe installed for better operational control over the filtration.

In filtration operations, the pulp 4, the volume of which is previouslymeasured, the reservoir 26 until the pre-established amount if reachedis introduced. Vacuum is applied through the conduit 31, which causes adifference in negative pressure in the vacuum chamber 29, which in turncauses the diaphragm 30 to close, thus depressurizing the vacuum chamber29. The vacuum then causes suction of the liquids, forcing them to passthrough the partition 28, situated below the mold 27, forming a filteredcake on said partition 28, throughout the mold 27. The residual liquidsremain accumulated in the vacuum chamber 29.

The filtration operation ends when there is no more overlying liquidover the filtered cake. At this moment, by turning off the vacuum bymeans of a meter placed at the vacuum conduit 31, the vacuum chamber 29is now under atmospheric pressure, releasing the diaphragm 30 andallowing the accumulated liquids to flow out.

The filtered cake may then be removed from the mold. For this purpose itis necessary to use mechanisms for turning the whole equipment withremoval by gravity of the cake on special trays.

The mold 27 may have any shape, provided that it will hold the pulpvolume that comprises the microfibers and the binding component(s).Particularly, the mold 27 has a rectangular shape with dimensions on theorder of 1.40 m×0.70 m. The container 26 may have any shape that isuseful for the equipment, that is, it may represent a spacecorresponding to the pulp volume that is to be worked on. The partition28, by preference, is a stainless-steel web in meshes from 60 to 200mesh-tyler.

The filtration operation does not imply settling processes, differingfrom the latter by its rapidity, and it is often possible to obtainfiltered pieces at intervals shorter than 3 minutes, depending upon thedegree of automation and adjust of the operations.

1. A microfibrous composition comprising: microfibrous siliceousspicules of spongiaria constituted by at least 98% of silicon dioxidewith average length of 200 μm and average thickness of 10 μm in anamount ranging from 70% to 99%, by weight, and at least a bindingcomponent in an amount ranging from 1% to 30%, by weight, the amountsbased on the total weight of the composition.
 2. A microfibrouscomposition according to claim 1, characterized by comprising an amountof siliceous spicules of spongiaria ranging from 90% to 99% by weight,based on the total weight of the composition.
 3. A microfibrouscomposition according to claim 2, characterized by comprising an amountof siliceous spicules of spongiaria ranging from 90% to 96% by weight,based on the total weight of the composition.
 4. A microfibrouscomposition according to claim 1, characterized by the fact that themicrofibers have a specific weight ranging from 2.0 to 2.2 g/cm².
 5. Amicrofibrous composition according to claim 1, characterized by the factthat the microfibers have a length-to-thickness ratio ranging from 10 to20.
 6. A microfibrous composition according to claim 1, characterized bythe fact that the microfibers are essentially constituted by silicondioxide.
 7. A microfibrous composition according to claim 1,characterized by the fact that the microfibers are transparent. 8.Microfibrous composition according to claim 1, characterized bycomprising an amount of binding component ranging from 1% to 10% byweight, based on the total weight of the composition.
 9. A microfibrouscomposition according to claim 1, characterized by the fact that thebinding component is selected from the group consisting of: aluminousclay, kaolinic clay, spectitic clay, mixed clay, colloidal clay andsilicic acid.
 10. A microfibrous composition according to claim 1,characterized by having a melting temperature ranging from 1250 to 1760°C.
 11. A microfibrous composition according to claim 1, wherein thecomposition has an apparent specific mass ranging from 0.06 to 1.20g/cm³.
 12. A microfibrous composition according to claim 11, wherein thecomposition has an apparent specific mass ranging from 0.40 to 0.60g/cm³.
 13. A microfibrous composition according to claim 12, wherein thecomposition has an apparent specific mass of 0.50 g/cm³.
 14. Amicrofibrous composition according to claim 1, wherein the compositionhas a porosity ranging from 45 to 95%.
 15. A microfibrous compositionaccording to claim 14, wherein the composition has a porosity of 70%.16. A microfibrous composition according to claim 1, wherein thecomposition undergoes a curing process.
 17. A process for obtaining amicrofibrous composition, characterized by comprising the followingsteps: a—mixing microfibers comprising microfibrous siliceous spiculesof spongiaria with average length of 200 μm and average thickness of 10μm with water and at least one binding component in an attrition tank;b—stirring said mixture until a homogeneous pulp is reached; c—shapingthe pulp in a shaping equipment to eliminate the excess water andbinding component and to obtain a residual cake; d—curing the residualcake by a curing process, obtaining the microfibrous composition.
 18. Aprocess according to claim 17, characterized in that, in the shapingequipment, the pulp undergoes a settling process.
 19. A processaccording to claim 18, characterized in that the settling process is asimple-type settling process.
 20. A process according to claim 18,characterized in that the settling process is a vibration-type settlingprocess.
 21. A process according to claim 17, characterized in that, inthe shaping equipment, the pulp undergoes a pressure-filtration process.22. A process according to claim 17, characterized in that, in theshaping equipment, the pulp undergoes a vacuum-filtration process.
 23. Aprocess according to claim 17, characterized in that the curing processis a drying in oven.
 24. A process according to claim 17, characterizedin that the curing process is drying in open air.
 25. A processaccording to claim 17, characterized in that the curing process is acalcination in furnace.
 26. A process according to claim 17,characterized in that the microfibrous composition undergoes a firingprocess.
 27. A process according to claim 26, characterized in that thetemperature of the firing process is higher than 800° C.
 28. A processaccording to claim 26, characterized in that, after the microfibrouscomposition undergoes the firing process, it undergoes a grindingprocess.
 29. A process according to claim 28, characterized in that thegrinding of the microfibrous composition is carried out with diamondsaws.
 30. A process according to claim 28, characterized in that thegrinding of the microfibrous composition is carried out with grindingwheels.